More than a million people have contributed to OpenStreetMap since its inception nine years ago, in patterns that look a little different depending on the city. In London, shown above, the street network has been mapped from scratch by many people, each hue in that picture reflecting a different user who has sketched a handful of streets or traced the outline of the buildings on one block. The map of London's mapmakers is a real mosaic, the reflection of aggregated efforts by many hands.
Zoom out, and all of Europe looks the same way:
Both of these pictures come from a new global map from MapBox and Eric Fischer that visually captures what it looks like behind the scenes when so many strangers each chip in a little (some of them a lot) to the world's largest open-source mapping repository. This atlas of all their efforts uses 65,536 hues (each covering a dozen contributors or so). Your eye, though, probably won't be able to tell each of them apart.
Compare that picture of London, though, to this one of San Antonio:
A more recently mapped city, San Antonio has been drawn in OpenStreetMap with a large import of Census Bureau TIGER data. After all that mustard yellow, some people have gone back in and manually added additional details.
San Francisco looks similar, with some additional care gone into plotting the building footprints of parts of town in popular transportation corridors:
Los Angeles, in contrast, more closely resembles London in the work of many contributors:
In Kuwait, Fischer points out, some people have appeared more interested in mapping certain kinds of roads or their own clearly delineated neighborhoods:
This picture of Brasilia is a similarly tidy one, revealing the neat separations of space and land use:
A less formally planned city like Kathmandu looks much more chaotic in this multicolored picture, where the street network itself is irregular and the neighborhoods mapped by individual people appear to blend into each other:
Those last two maps in particular hint at the connection between underlying urban form and how mapmakers respond to the challenge of drawing it. Fischer offers this hypothesis via email:
When you have a city with a highly formal structure, it is possible to map it in a fairly abstract way: first put in the major highways, then arterials, then fill in the neighborhood detail. When you don't have a visible structure like that, it's much harder to do "armchair mapping" from afar. You can't tell how things actually relate to each other unless you are there to observe them yourself, so people map outwardly from the places they know rather than inwardly from a larger framework.
For all the ways there are to design cities, there are as many ways to crowdmap them:
All maps courtesy of MapBox and Eric Fischer.